Method of and apparatus for storing liquefied gas mixtures



.March 21, 1944, DANA ET 2,344,765

METHOD OF AND APPARATUS FOR STORING LIQUEFIED GAS MIXTURES Filed Jan.14, 1941 INVENTORS LEO l.-DANA GEO GE H. ZENNER ATTORN EY liquid willPatented Mar. 21,

UNITED STATES PATENT OFFICE amass METHOD OF AND APPARATUS FOR STORINGLIQUEFIED GAS MIXTURES apparatus for storing Leo 1. Dana, Buiialo,

more, N. Y., nets Company,

and George B. Zenner, Kenasslgnors to The Linde Air Pro!!- a corporationoi Ohio Application January 14, 1941, Serial No. 874,330

I 4 Claims- (Cl. 62-1) This invention relates to a method of andliquefied gas mixtures at relatively low temperatures and moreparticularly to a method of and apparatus for maintaining substantiallyconstant, the

proportions of the constituents of a mixture of gases, when gas isdischarged irom an insulated container holding a body of the gas mixtureat the liquid state.

When liquefied gases containers at relatively low temperatures,atmospheric temperature,

low temperature in stored in insulated below some leakage of heat areinto the stored liquid inevitably occurs because the commerciallyavailable insulating means employed in such containers does not excludeall heat tending to enter the liquid from the environment. Thus a smallamount of liquid will constantly in the gas space above is necessary tovent gas tend to evaporate and build a pressure the liquid in thecondevelop, it from the container to prevent an excessive rise inpressure.

When a mixture of liquefied gases having different boiling points, suchfor example, as a 'liquefied gas having mixed therein a small proportionof another liquefied gas of difierent boiling point is stored, theevaporation due to heat leak causes the gas produced to have arelatively difierent composition than that of the liquid because thecomponent having the lower boiling point will tend to evaporatepreferentially so that the composition of the vapor as well as thecomposition of the remaining liquid will change,

the vapor produced and vented being initially richer in the componenthaving the lower boiling point and the liquid remaining in storagebecoming richer in the higher boiling point.

cial practice.

According to composition or purity of component having the Suchvariation of composition is in general quite undesirable in commertheinvention such changes of both gas withdrawn and liquid stored areprevented and the effects of heat leaks into a container having a bodyof liquefied gas are counteracted by withdrawing a small quantity ofliquid from the main body of liquid, and evaporating completely suchwithdrawn liquid in a manner that prevents an excessive rise inpressure. The vapor so evolved evaporation of the be of the samecomposition as the by complete small quantity liquid and there will beno undesirable difference oi composition or'purity.

It is a principalpbiect of the present invention 5 of gases when toprovide an improved method of and apparatus for storing mixtures ofliquefied gases at relatively low temperatures. Other objects 0! theinvention are: to provide a method of and apparatus for maintainingsubstantially constant the proportions of the constituents of a mixturestored in the liquefied state; for maintaining the proportions of theconstituent gases relatively constant when evaporating a mixture ofliquefied gases; to provide a method of and apparatus for counteractingthe efiects of heat leak into a stored body of liquefied gas ofcommercial purity by causing such heat to completely vaporize a portionof liquid separated from the stored body of liquid in a manner such thatan excessive rise of pressure is prevented and the composition andpurity of the vapor produced and the stored body of liquid remainssubstantially constant; and formaintaining substantially constant thepurity of. commercial oxygen supplied in both gaseous and liquid statesfrom an insulated container in which is stored a body or liquid oxygenat low temperature. These and other objects and novelfeatures of thisinvention will become apparent from the following description and theaccompanying drawing, in which:

Fig. 1 is a sectional view of an exemplary con tainer for holding a bodyof liquid oxygen including means for maintaining the purity of gasdischarged therefrom substantially constant according to the principlesof the present invention; and

Fig. 2 is a fragmentary sectional view on an enlarged scale of analternative form of expansion valve.

The principles of the invention will be set forth in connection withmeans for storing commercial liquid oxygemas an example of a mixture ofliquefied gases which by customary storage arangements would have a gasphase above the liquid of dlflerent composition than the liquid.Commercial liquid oxygen generally and preferably contains 99.6% pureoxygen; the remainder consisting of mainly liquid argon and nitrogen.The boiling points of oxygen, argon and nitrogen at normal atmosphericpressure are --183 C., 186 C. and 196 C., respectively. Commercialliquid oxygen thus constitutes a liquefied gas mixture in which theconstituents have substantially difierent boiling points and whencommercial liquid oxygen is stored in the customary insulated container,the slow inflow of heat through theinsulatlon to the liquid causes a.slow but constant evaporation ,of liquid to occur. The vapor thataccumulates in the gas space above the liquid in the container is richerin on and nitrogen than the liquid. Thus, when it is desired ornecessary to draw vapor from the gas space of such a container toprevent excessive rise of pressure, the gas withdrawn will not comprise99.6% oxygen but will be of lower purity. It is desirable that all thegas material in both liquid or gas phases withdrawn from the storagecontainer for commercial use should be of a constant purity.

According to the present invention, the heat leak that normally occursinto a body of stored liquid oxygen is compensated for or removed fromthe container by withdrawing portions of liquid of constant compositionfrom below the surface of the stored body of liquid and evaporato Fig.1, a body of liquefied gas, for example,

commercial liquid oxygen is indicaated at l0, stored within a metalvessel II which may of any suitable shape, for example, cylindrical orspherical. The vessel II is surrounded by a relatively thick layer ofheat insulating material l2 which may be or any customary type such as avacuum insulation or a dry powdered material. The insulation is heldwithin an outer casing l3. Suit able means for adding and withdrawingliquid oxygen are provided in the form of a liquid line I connectingwiththe bottom of the vessel II and leading to a point outside of the casingl3. A gas phase withdrawal line l5 connectin with the top of the vesselII is also provided. A branch of the line I5 is preferably provided witha safety or pressure relief valve l6. It is also desirable to provide apressure gauge Il connecting with the vessel II to indicate the pressuretherein. The means for maintaining the purity constant comprises aneduction tube l8 leading from a point within the body of liquid ill toan expansion valve i9 having an operating handle 20. From the dischargeside of the expansion valve ii), a connection 2| conducts liquid to anevaporating coil or condenser 22. The condenser 22 may be of anysuitable form providing suflicient heat transfer area such as a tubularsection having external heat transfer fins 23. The condenser 22 ispreferably disposed within the gas space above the body of liquid III.From the other end of the condenser 22, a connection 24 passes throughthe wall of the vessel II to a trap 25. The trap 25 comprises a smallchamber from the top of which the evaporated gas is withdrawn ordischarged through a pipe 26. The trap 25 is provided with upper andlower connections 21 and 28 leading to a liquid level gauge 29 which isprovided to indicate the presence of liquid in the trap 25. The gaswithdrawn through pipe 26 may, if desired, be conducted to a gas holderor to a compressor for charging the gas into storage cylinders or, gaswithdrawn through connection 26 may be delivered to oxygen consumingapparatus that requires the oxygen to be of the standard purity becausethe purity of such evaporated liquid will be substantially constant andthe same as the purity of the main body 01' the liquid l0.

In operation a body or liquid in is introduced into the storagecontainer II which preferably is constructed to withstand only arelativel low internal pressure above atmospheric pressure. As heatleaks through the insulation i2 and reaches the liquid ill, some bf theliquid will evaporate and tend to build a pressure in the space abovethe liquid. Such pressure will be indicated on the pressure gauge ll.When the desired safe upper limit of pressure is reached, a pressure ismaintained in the pipe 26 01' a value that is lower than the pressure inthe vessel H, such as by connecting the pipe 26 to a low-pressure gasholder or to the suction side of a pump. The expansion valve i9 isopened by the operation of the handle 20 to a degree sufllcient to allowliquid to pass up through the eduction tube I8, become expanded inpassing through the valve 19 and flow into the condenser 22. Under theefiect of the reduction of pressure, which lowers the boilin point ofthe liquid, the liquid passing into the condenser 22 will boil at theexpense of heat absorbed from the vapors in the space above the liquidl0. Due to such heat exchange, a portion of the vapors which arise fromthe surface of the liquid I 0 will become recondensed and fallback tothe body of liquid. In this manner the heat that enters the liquid I0after the predetermined pressure has developed is removed by thecondenser 22. The vapors produced in the condenser 22 pass through theconnection 24 and the line 26. If the valve i9 is opened too much so asto pass liquid at too great a rate, some liquid will pass out throughthe connection 24 and begin to accumulate in the trap 25. Suchaccumulation will be indicated by the liquid level gauge 29 and theoperator will then reduce the flow by closing the valve I9 slightly.

If desired, the valve l9 may be replaced by an automatically operatedvalve i9 as shown in Fig. 2, which valve is caused to open by a rise ofpressure in the vessel ll. Such automatic valve I8 may be of anysuitable construction and may comprise a valve body 30 having a porttherein controlled by aneedle valve 3|. The needle valve 3| is connectedfor operation to a diaphragm 32, the underside of which is exposed tothe pressure of the vessel I I by connection with the vessel through aconduit 33. The valve is urged to the closed position against the actionof the diaphragm by an adjustable spring 34 and the valve stem 3| may besealed by a bellows 35 having one end secured to the body 30 and theother end secured to the stem of the valve 3!. It will be evident thatwhen the pressure in the vessel ll rises, the diaphragm 32 will be movedupwardly against the force of the spring 34 and the valve 3| will belifted from its seat. When sufficient liquid has passed through thevalve casing 30 from the inlet ill to the outlet connection 2|, thepressure in the gas space above the liquid ill will be reduced due tocondensation of gas. This will cause the pressure in the vessel to dropand allow the valve 3i to close and thus automatically maintain thepressure in the vessel substantially constant.

The embodiments described herein and illustrated in the drawing aredisclosed to indicate how the invention may be applied. Certain featuresof the invention may be used independently of others and changes may bemade in the details of the apparatus without departing from theprinciples of the invention. Due to the difference of pressure, theportions of liquid that are passed into the vaporizer 22 will boil at alower temperature than the main body of liquid, thus a pressure riSe canbe prevented by permitting a flow of liquid into the vaporizer at a ratesum-- cient to balance the heat leak into the storage vessel. It is alsocontemplated that the vaporizer may have the form of a pipe coilarranged in heat conducting relation to the outside surface -of theliquid holding vessel H, and in any embodiment of the invention therefrigeration still contained in the gas discharged through the conduit26 may be usefully applied to cool the insulation I2 by passing the gasthrough a tube disposed in the insulation I2 in a manner similar to thatproposed in U. 8. Patent No. 1,866,514 of C. W. P. Heylandt.

We claim:

1. Apparatus for storing a mixture of liquefied gases at low temperaturewhich comprises a container for holding a body of such liquefied gases;heat insulating means surrounding said container; means for withdrawingportions of said body or liquid; means for expanding such withdrawnportions of liquid; a condenser disposed entirely in the vapor space ofsaid container for vaporizing said expanded withdrawn portions of liquidin heat exchanging relation with vapor above the liquid stored in saidcontainer; and a conduit connected to said condenser for conducting awaythe vapors or said vaporization for use.

2. Apparatus according to claim 1 in which said expansion meanscomprises a valve operable in response to a pressure increase in saidcontainer.

3. Apparatus according to claim 1 including means interposed in saidconduit for indicating the outflow of unvaporized liquid with gasdischarged through said conduit.

4. Method of maintaining substantially constant the composition andpurity of a valuable gas mixture when stored in the liquid state in aninsulated container at a relatively low temperature and below apredetermined pressure which comprises, withdrawing regulated portionsof said liquid; completely vaporizing such withdrawn portions of liquidby heat exchange with vapors above the surface of the stored liquid;withdrawing for use the vapors of such vaporization; and regulating saidliquid withdrawal and said vaporization at a rate sufllcient to maintainthe pressure of said vapors above the stored liquid below saidpredetermined pressure, whereby the temperature and composition of thestored liquid is maintained substantially constant and the compositionof the vapor withdrawn is maintained the same as the composition of saidstored liquid.

' LEO I. DANA.

GEORGE H. ZENNER.

